Bicycle cargo carrying racks, also known as pannier racks, luggage racks or carrier racks are ubiquitous cycling accessories used all over the world. They come in various different forms and are often positioned over either the front or rear wheel.
The purpose of a cargo rack is to allow a cyclist to carry cargo upon the frame rather than on their person. Cargo racks are generally shaped to allow cargo to be carried either in the form of a pannier pack or directly upon the rack.
The design of a cargo rack must consider many different functional aspects. These include:
What range of bicycles it can connect to
How the rack connects to the bicycles
How the rack connects pannier bags
What load it is capable of carrying
How the rack is stored pre-purchase or post-purchase
During use, the forces that are transmitted through the rack and on to the bicycle can be considerable. There may be vertical loads whilst overcoming bumps in the road, front to rear loads experienced during acceleration and deceleration and finally lateral loads as the user swings the bicycle whilst pedalling. If a load is not rigidly connected to the frame it may sway therefore making it more difficult to control the bicycle. The stiffness and strength of a cargo rack and the rigidity of the connection therefore has a serious impact on ride quality. It is this primary function that therefore defines the form of existing cargo racks.
Rear cargo racks can be generalised in to two different categories—those which mount to the frame and those that mount only to the seat post. The former tends to be a truss-like structure with multiple connection points whilst the latter is a cantilevered structure.
U.S. Pat. No. 4,154,382, issued May 15, 1979 and entitled “Bicycle Rack” describes and illustrates a cargo rack manufactured from welded, bent rod which is strong, stiff and terminates in appropriate connection points that result in a rigid truss like structure.
Truss like cargo racks are designed to mount to the frame and do so usually by connecting to four locations with the use of threaded fasteners. The two lower locations are usually on the frame ‘dropouts’. The upper two locations are usually on the seat stays or tube. These types of cargo racks are popular because they have a high load limit and are inexpensive. However these racks also have various drawbacks:                They require tools to secure the rack which, in turn, precludes them being considered ‘quick-release’        They require the frame to have the necessary mounting points and threaded holes        To achieve a rigid structure the rack is often welded in the final shape which is bulky and does not transport or store easily        
If a frame does not have the necessary upper mounting points then there are various methods to create fixation points. One option is to use pipe clamps, U-bolts, P-clips and the like upon the seat stays. Another method is to use a seat clamp with additional protrusions and threaded holes. While these means for attaching accessories to a bicycle do have utility, the drawbacks are numerous:                Still requires tools to attach        Excess weight        May be considered unsightly        If a member of a bicycle frame is not in an assumed orientation or where the frame member is of a different size or shape attachment may not be possible        When used on frames manufactured from a carbon-fiber composite then damage can occur with incorrect clamping forces        
If a frame does not have the necessary, lower mounting points then there are also various solutions. The first solution is to thread the skewer through the lower mounting holes of the rack. Another options is the use additional plates that are sandwiched either side of the frame with the skewer. These plates contain threaded holes to allow attachment. These solutions have some of the following negative points:                Protrusions on the frame can cause an interference stopping assembly        Different load scenarios can cause undesired stresses on the skewer, frame or rack        Complex assembly        Excess weight        
US Patent Number US2012/0168479, issued Jul. 5, 2012 and entitled “Cantilever bike rack” describes and illustrates a cargo rack manufactured from a combination of welded rod & tube which terminates at the seat tube that results in a cantilevered structure.
The benefit of a seat-post mounted cargo rack is the ability to mount to almost any bicycle although usually this is dependent on the bicycle having a round seat-post. There are however various downsides:                They have a limited ability to carry heavier loads due to concerns around frame, seatpost or seat damage        Cantilevered structures can be heavier than truss-like structures when comparing them in a like-for-like weight carrying scenario        The connection to the seat-post must be extremely secure to stop side to side slip therefore the usually results in a bulky clamp-like assembly        
Finally, whatever the type of cargo rack that is utilized it is usually expected that a pannier bag will attach to a substantially horizontal member upon the rack. U.S. Pat. No. 5,673,833, issued 7 Oct. 1997 and entitled “Device for holding bags on bicycles, motorcycles and the like” describes and illustrates a method for securing a bag to a rail of a cargo rack. The attachment method as described in the patent are acknowledged to be of high quality, however, there various disadvantages.                Must have at least two points of contact separated by a distance        Dictates that the cargo rack must have a horizontal member        The horizontal member must be substantially round        
If the horizontal member is not the correct diameter, then there will be a loose fit to the pannier
Although the fastening rail is rigid the connection the bag itself is not